1. Field of the Invention
This invention relates generally to an electrical contact or an electrical contact assembly typically used in an electromechanical device and, more particularly, to a contact or contact assembly that utilizes carbon fibers in various forms as the element that makes electrical contact with another element of the electromechanical device.
2. Description of Background
Variable resistive devices utilize elements that vary a voltage or current in order to provide an electrical signal that indicates a relationship to a physical position of a contact or wiper on a resistive or conductive element. Because these variable resistive devices are used in a dynamic state they can not be fixed or restricted in their movement and must have the freedom to be positioned along any length of their respective resistive or conductive paths. The contact or wiper must therefore be produced of a material that is electrically, physically, and environmentally compatible with the resistive and/or conductive track when in the presence of an electrically active and physically dynamic system. The contact or wiper must also provide a long useful life, while maintaining uniform positive engagement with the resistive or conductive element and not produce polymers or debris which acts as an insulator and distorts the output signal.
Presently the contact or wiper materials used for these variable resistive devices are composed of various clad or coated metals or precious metal alloys. These precious metal containing contacts in a dynamic state and in the presence of electrical activity act as catalysts to generate polymers and debris which degrade the resistive track output signals. This results in the early termination of accurate performance and useful life.
Initially metal contacts or wipers were used with wirewound resistive or metallic conductive elements, because wirewound elements were the most precise devices. As time evolved great improvements were made in the non-wirewound product area, and they supplanted the wirewound resistive element, but the contact or wiper has always created problems relative to the resistive element because in the presence of an electrical current and dynamic performance, the precious metal components of the metallic contact provide the catalyst to generate polymers and debris, which interfere with the accuracy of the output signal.
Now that reduction in size, improved accuracy, and a reduction in electrical contact resistance are required in modern servo feedback positioning systems, non-metallic contact materials must be considered to obtain the necessary and sorely needed improvements in these performance characteristics and elimination of the polymers and debris.
Accordingly, the need exists for improvements in electrical contacts and contact assemblies and, particularly, for improvements in the materials and assemblies employed therefor.
Accordingly, it is an object of the present invention to provide a contact or contact assembly for use in electromechanical applications that can effectively eliminate the above-noted defects inherent in previously proposed systems.
It is another object of this invention to eliminate the above-described negative conditions and characteristics of previously known systems and to improve considerably the useful life of the system by providing a contact or wiper formed of nonmetallic material, such as one composed of carbon fibers. This carbon fiber material, through special processing, not only overcomes the negative conditions caused by metal composition contacts or wipers, but considerably improves total performance in all other aspects.
It is a further object of the present invention to provide a wiper contact or contact assembly for use in electro-mechanical components or applications that is more compatible with present state of the art fabrication techniques and materials used for resistive and conductive track substrates and that appreciably reduces or eliminates the negative aspects inherent in presently used or previously proposed designs or materials.
In accordance with one aspect of the present invention an existing contact carrier is employed and in place of the previously used metal contacts, carbon fibers are employed that are specially attached to a carrier.
According to one aspect of the present invention, a nonmetallic electrical contact, such as one made of carbon fiber material, is processed and formed in such a manner as to allow the multiple strands of carbon fiber when properly positioned to be electrically conductive for transmitting umimpeded electrical signals along its longitudinal length. Such carbon fiber strands may be fused or conductively bonded by any of various techniques to provide essentially uniform conductivity and redundant transmission of the electrical signal. The carbon fiber material can be affixed to a carrier or the fibers may be utilized without a carrier. Such a carrier, if used, may be metallic or non-metallic and may be affixed to the carbon fiber bundles by any of various bonding, fusing, and fastening techniques. The carrier can also be electrically nonconductive, depending upon the application. Alternatively, the carrier can be formed of the same homogenous carbon fiber material as that used for the actual contact. Forming of the carbon fiber contact can involve cross-layering of the material in nonparallel orientations to provide additional structural integrity, as well as to assist in the postforming operation.
The inventive wiper contact is rigid enough to sustain and maintain a consistent position relative to its parallel alignment to the resistive or conductive track of the substrate element and yet is flexible enough in a perpendicular position to the track to allow some variation in movement to sustain uniform contact position, spring rate and pressure. Thus, the electrical output signal maintains its integrity.
A further aspect of the present invention is that the contact surface of the wiper contact that is adjacent to the resistive or conductive track is composed of multiple points of contact, rather than either a small number of metal fibers or just one broad band of a rigid beam contact. This ensures a more redundant positive footprint with the resistive or conductive track, which reduces contact resistance and variable electrical noise.